In recent years, studies for miniaturization and power saving of sensors have been conducted. In general, a sensor requires a power supply for operation, and in a case of using an external AC power supply, there is a difficulty in achieving miniaturization because a transformer and a rectifier capacitor are large. On the other hand, there are some sensors using button batteries, but butteries require maintenance such as changing, and therefore a problem also arises assuming that they are mounted inside electrical equipment.
A sensor that resolves such difficulties has been proposed in NPL 1. This sensor utilizes energy harvesting, by which energy is derived from the surroundings of AC power lines, and uses a TDC (Time-to-Digital Converter), thereby enabling real-time measurement and data transmission with limited energy.